MOVEMENTS OF TENTACLES IN ACTINIANS 107 



this form of polarity can be based, a most simple relation is 

 discoverable. As Groselj ('09, p. 290) has pointed out, the nerve 

 fibrils that arise from the sense cells in the tentacles of actinians 

 extend as a rule in a direction corresponding with the length of 

 the tentacle. In Bunodes many of these cells are bipolar and 

 in that case one fibril extends distally along the tentacle and the 

 other proximally, but there are also in this actinian a goodly 

 number of cells that are unipolar and in such instances the fibrils 

 almost invariably extend toward the base of the tentacle. In 

 Cerianthus almost all the sense cells in the tentacular ectoderm 

 are unipolar and their fibrils run almost without exception toward 

 the base of the tentacle. As these fibrils transmit impulses 

 away from the cell bodies with which they are associated, it 

 follows that in both these actinians transmission must be pre- 

 dominantly toward the base of the tentacle and that conse- 

 quently the region of response would be largely proximal to the 

 region of stimulation. This is what is to be seen in the neuro- 

 muscular reactions of most actinian tentacles and I, therefore, 

 believe that the polarity of these organs, as evidenced in the proc- 

 esses just mentioned, is dependent upon the proximal direction 

 taken by the sensory fibrils in these structiu-es whereby the nerv- 

 ous impulses are led to flow predominantly toward the base of 

 the tentacle (Rand, '09, p. 235). This anatomical interpreta- 

 tion of the polarity of the tentacle is supported by the observa- 

 tion made by Chester ('12, p. 468) that after two tentacles of 

 Metridium have been grafted together base to base there is no 

 change in their (ciliazy or) muscular polarity. 



Concerning the relation of the tentacle to the organization of 

 the animal as a whole, the preceding discussion must make sev- 

 eral points clear. In Condylactis the tentacle is filled with fluid, 

 whose shght pressure is dependent upon the activity of the body 

 as a whole. It also receives from other parts of the animal 

 thi'ough its base nervous impulses by which its neuromuscular 

 mechanism may be set in operation, though this process is much 

 more generally accomplished by the direct stimulation of the 

 tentacle itself. Aside from the supply of nutriment transmitted 

 to the tentacle from the general store produced in the gastrovas- 



